Food intake in humans is often thought to be under the control of sociocultural, cognitive, sensory and other external factors. Physiological factors controlling food intake are usually not emphasized in explanations of human eating behavior. There is evidence that food intake in humans may be under a postabsorptive control responsive to the availability and metabolism of circulating nutrients; however, because of various methodological limitations this evidence is not conclusive. Based on the results of preliminary studies, we proposed experiments to examine the effect of intravenous feeding on food intake in healthy male volunteers. One aspect of these studies will involve an examination of subject-and experiment-related factors which affect food intake under our experimental conditions. We will also determine whether the compensatory reduction in voluntary food intake observed during intravenous feeding is a response to specific nutrients or a response to calories. The restoration of food intake after cessation of intravenous feeding will be examined with respect to time course and role of prior nutrient infusion. We will also determine whether intravenous feeding reduces intake of a normal, varied diet as it does a liquid diet. Finally, we will determine whether subjects can maintain caloric intake by self-administration of intravenous nutrients. These studies will provide basic information on the postabsorptive control of food intake in humans. In addition, these experiements may help to explain problems in appetite and difficulties in the transition from intravenous to oral feeding in patients recieving parenteral nutrition.